Clean water is one of the most fundamental resources for human kind. In reality the ground water gets contaminated with various contaminants. Chromium is one of the very common contaminants, as it is released as effluents from industries of electroplating, leather taming, and corrosion protection. Chromium exists in several valence states viz., Cr (VI) and Cr (III). The hexavalent chromium (Cr (VI)) in ground waters is known to be environmentally hazardous (Blowes, 2002 Science v 295, 2024). Chromium (VI) is highly toxic and mobile whereas Cr (III) is insoluble and nutrient in small amount and not hazardous.
Reference may be made to a publication by Taylor et al., 2000, Clays and Clay Minerals, v48, 648, wherein the hexavalent chromium is reduced by dithionate clays. The major drawbacks are that Chromium ions are adhered to sodium dithionate which can be washed of freely and the compilation of inadequate data in terms of its application.
Reference may be made to a publication by DrIjaca et al. 1992, Inorg. Chemistry, v31, 4894, wherein the trivalent Cr is strongly sorbed by montmorillonite, for the effective removal of Cr from pollutant environments. The drawback is the technique deals only with trivalent Cr, which are less toxic compared to the hexavalent Cr.
References may be made to publication by Kim et al., 2002, Environmental Geology, v42, 642 wherein the reduction of hexavalent chromium is effected by hydrothermally altered andesite containing 11.8% of pyrite. The draw backs are that pyrite-rich andesite is an effective reductant only in KCl and K2SO4 and also the absence of data on the quantity of reduced chromium in that publication.
References may be made to publication by Parthasarathy et al. 2003, American Mineralogist, V 88, 1983, also Patent 0272 DEL2003 fled during 2002, wherein the possible reduction of hexavalent chromium is discussed. The draw backs are that they do not describe any techinical detail of the conversion and the maximum conversion is about 50 to 60 wt %.